Methods and systems for synthesis on nanoscale materials

ABSTRACT

A method and apparatus for production of nanoscale materials is disclosed. In the preferred embodiments, the invention is scalable and tunable to reliably produce nanoscale materials of specifically desired qualities and at relatively high levels of purity. In a preferred embodiment, combustible gas is discharged onto a substrate through a multi-zone flame facilitating the formation of nanoscale materials such as single and multi-wall nanotubes.

RELATED APPLICATION DATA

This application claims the priority of prior provisional U.S. patentapplication Ser. No. 60/671,001, filed on Apr. 13, 2005, whichapplication is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates nanoscale materials, and more particularlyrelates to methods and apparatuses for the flame synthesis of highpurity carbon nanotubes and other novel nanoscale materials. Theinvention is believed to offer significant potential for manufacturingof carbon nanotubes and the like in large quantities at substantiallylower cost than that of other methods currently available. Thisinvention allows for the selective synthesis of single-wall (SWNTs)and/or multi-wall (MWNTs) nanotubes with specific dimensions andproperties by controlling the catalyst size. Carbon onions and/or highpurity nanodiamonds can also be produced. Further, the inventionprovides for continuous processing and commercial scalability based onintegrating known practices in the carbon black industry.

BACKGROUND OF THE INVENTION

Carbon nanotubes are tubules of carbon generally having lengths from 5to 100 micrometers and diameters from 5 to 100 nanometers. Carbonnanotubes may be formed as one SWNT (single-walled nanotubes) or severalco-axial cylinders of graphite sheets MWNT (multi-walled nanotubes).Carbon nanotubes can function as either a metallic-like conductor or asemiconductor, according to the rolled shape and diameter of the helicaltubes. (Ebbesen II; Iijima et al., “Helical Microtubules Of GraphiticCarbon,” Nature, Vol. 354, (1991) 56).

Carbon nanotubes have many desirable physical, chemistry and electronicproperties such as: a high mechanical strength (Young modulus+1 TPa)with low weight compared to volume (2.0 g/cm³); high specific area(100-250 m²/g); high aspect ratio and chemical stability; high thermalconductivities and excellent photoemission properties, among others.

Nanotubes comprised of, or doped with, other atoms are proving to haveequally interesting physio and photo electronic properties. (J. Bai, et.al. “Metallic single-walled silicon nanotubes” in Publications of theNational Academy of Sciences, 2004, 101(9), 2664-2668; D. F. Perepichkaand F. Rosei “Silicon Nanotubes” in Small, (Wiley Press) 2006, 2(1),22-25).

Currently, there are many emerging materials applications awaitingcommercialization of such nanoscale materials. For example:

1. Composites

As conductive filler in polymers, CNTs are quite effective compared totraditional carbon black micro-particles, primarily due to their largeaspect ratios (Colbert D T. “Single-wall nanotubes: a new option forconductive plastics and engineering polymers.” Plastics AdditivesCompounds, 2003, 18-25).

CNTs may also be used in composites for thermal management (Biercuk M J,Llagumo M C, Radosvljevic M, Hyun J K, Johnson AT. “Carbon nanotubescomposites for thermal management.” Appl. Phys. Lett 2002, 80, 15.).

CNTs may be used as reinforcement for polymer matrices or rubber matrix(Meincke O, Kaempfer D, Weickmann H, Friedrich C, Vathauer M, Warth H.“Mechanical properties and electrical conductivity of carbon-nanotubefilled polyamide-6 and its blends with acrylonitrile/butadiene/styrene.”Polymer 45, 2004, 739-748)/(Frogley M D, Ravich D, Wagner H D.“Mechanical properties of carbon nanoparticle-reinforced elastomers.”(Composites Science and Technology 63, 2003, 1647-1654).

CNTs may be dispersed into matrices of conjugated polymers, such aspoly(phenylenevinylene) and derivatives, to prepare composites ofinteresting optoelectronic properties. (Dalton A B, Stephan C, Coleman JN, McCarthy B, Ajayan P M, Lefrant S, Bernier P, Blau W J, Byrne H J.Journal Phys. Chem. B 104, 2000, 10012).

2. Field Emission

Both B- and N-doped CNTs may have great potentials as building blocksfor stable and intense field-emission sources. Electrons can be easilyemitted from CNT tips when a potential is applied between the CNT'ssurface and an anode. N-doped MWNTs are able to emit electrons atrelatively low turn-on voltages (2 V/μm) and high current densities(0.2-0.4 A/cm2) and shown excellent field emission properties at 800 K.

Their size with high aspect ratios and small tip radius of curvatureleads to possible use as electron emitters for flat panel displays andAFM/STM probes. (Q. H. Wang, A. A. Setlur, J. M. Lauerhaas, J. Y. Dai,E. W. Seelig, and R. P. H. Chang, Appl. Phys. Lett. 72, 1998, 2912) and(H. Dai, J. H. Hafner, A. G. Rinzler, D. T. Colbert, and R. E. Smalley,Nature 384, 1996, 147).

3. Sensors

Pure carbon SWNTs and MWNTs can be used to detect toxic gases and otherspecies, because small concentrations are capable of producing largeshifts in the nanotube conductance, shifting the Fermi level to thevalence band, and generating hole-enhanced conductance. CN_(x) MWNTsdisplay a fast response on the order of milliseconds when exposed totoxic gases and organic solvents and reach saturation within 2-3seconds.

4. Alternative Energy Storage Devices

A particularly interesting property of carbon nanotubes is that theirwidths are just large enough to accept hydrogen molecules but too smallfor larger molecules. As a result, carbon nanotubes have drawn a greatdeal of attention as storage vehicles for hydrogen and, consequently,for use in fuel cell applications.

Although carbon nanotubes have many advantageous properties, successfulcommercial applications of them have not yet been reported due to thedifficulty in synthesis capacity, manipulation and structuralcontrollability of the carbon nanotubes. Therefore, there is a need fora method and apparatus which enables the synthesis of uniform highpurity carbon nanotubes and other nanoscale materials in a costeffective and easily controllable method.

Synthesis of Carbon Nanotubes

1. Catalytic Disproportionation of Carbon Monoxide

Carbon nanotube synthesis was reported in the 1970's and 80's using thecatalytic disproportionation of carbon monoxide and/or hydrocarbons. (R.J. K. Baker, et. al “Formation of Filamentous carbon from iron, cobaltand chromium catalysed decomposition of acetylene” Journal of Catalysis,1973, (30), 86-95.) The resulting nanotubes were well-characterized assuch by high resolution transmission electron microscopy and x-raydiffraction spectroscopy. (M. Audier, A. Oberlin, M. Oberlin, M. Coulon,and L. Bonnetain in Carbon, 1981, (19), 217-224). However, the work byearly researchers was not to be fully understood in the current conceptof so-called ‘carbon nanotubes’ until the discovery of Buckminsterfullerene (C60), a new allotrope of carbon in 1988, followed by lijma'sreport in 1991 of the ‘discovery’ of carbon nanotubes, another ‘new’allotrope of carbon.

Later work by Smalley et. al in the 1990's used the dispropotionation ofcarbon monoxide under high pressures with metal catalysts. Known as the“HiPCO” process, it was one of the first attempts at production of SWNTson a batch scale level.

2. Arc Discharge Techniques

Those of ordinary skill in the art will appreciate that carbon tubulescan be prepared (with some degree of efficiency and quality, at least)using standard arc-discharge techniques. Generally, the discharge is ina reaction vessel through which an inert gas flows at a controlledpressure. The potential, either direct current (DC) or alternatingcurrent (AC), is applied between two graphite electrodes in the vessel.As the electrodes are brought closer together, a discharge appearsresulting in plasma formation. As the anode is consumed, a carbonaceousdeposit forms on the cathode, a deposit that under the proper conditionscontains the desired carbon nanotubes. Carbon nanotubes produced by anarc discharge between two graphite rods were reported in an articleentitled: “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354,Nov. 7, 1991, pp. 56-58) by Sumio Iijima.

This technique is commonly used to produce carbon nanotubes, however,yield of pure carbon nanotubes with respect to the end product isregarded by some as less than optimal, i.e., only about 15%. Thus, acomplicated purification process must be carried out for particulardevice applications. (J. Kong, A. M. Cassell, and H Dai, in Chem. Phys.Lett. 292, 567 (1988)).

A variation of this general synthetic procedure is reflected in U.S.Pat. No. 5,482,601, wherein carbon nanotubes are produced bysuccessively repositioning an axially extending a graphite anoderelative to a cathode surface, while impressing a direct current voltagethere between, so that an arc discharge occurs with the simultaneousformation of carbon nanotubes as part of carbonaceous deposits on thevarious portions of the cathode surface. The deposits are then scrapedto collect the nanotubes. The anode must be repositioned respective tothe cathode, repeatedly, to provide larger quantities of the desirednanotube product.

However, conventional methods of making multi-walled nanotubes via arcdischarge do not easily lend themselves to large scale production. (D.T. Colbert, J. Zhang, S. M. McClure, P. Nikolaev, Z. Chen, J. H. Hafner,D. W. Owens, P. G. Kotula, C. B. Carter, J. H. Weaver, A. G. Rinzler,and R. E. Smalley, Science 266, 1218 (1994)).

2. Laser Ablation Techniques

The laser vaporization method, which had been originally used as asource of clusters and ultrafine particles, was developed for fullereneand CNTs production by a group led by Richard E. Smalley. (A. Thess, R.Lee, P. Nikolaev, H. Dai, P. Petit, J. Robert, C. Xu, Y. H. Lee, S. G.Kim, A. G. Rinzler, D. T. Colbert, G. E. Scuseria, D. Tomanet, J. E.Fischer, and R. E. Smalley in Science, 273, 483 (1996)).

CNTs were grown by laser ablation of graphite composite targets atdifferent temperatures under argon flow. Ni and Co have been used as oneof the catalytic materials for formation of SWNTs during laser ablation.The target was fixed inside a quartz tube, which was fitted in anelectric furnace. The tube was first evacuated by a rotary pump, andthen flowing argon gas was introduced in it. The pressure of argon gasinside the tube was maintained at 500 Torr. The target and the growthzone were heated by an electric furnace. The method has severaladvantages, such as high-quality SWNT production, diameter control,investigation of growth dynamics. (J. Hafner, M. Bronikowski, B.Azamian, P. Nikoleav, D. Colbert, K. Smith, and R. Smalley, in Chem.Phys Lett. 296, 195 (1998); R. Sen, S. Suzuki, H. Kataura, Y. Achiba.Chemical Physic Letters 346, 2001, 383.)

3. Plasma-Assisted Chemical Vapor Deposition (CVD)

Radio frequency (RF) plasma or microwave plasma-enhanced chemical vapordeposition techniques have been used to synthesize large areas ofaligned MWNTs. In general, the apparatus of these techniques consists ofa quartz tube, a furnace for heating a substrate, a waveguide, and apumping system. These techniques work at base pressure (10⁻² Torr). Thesubstrate is placed in the quartz tube heated in the furnace. Thistechnique using Fe and/or Ni as transition metal catalysts dispersed onsilica substrates. Acetylene or CH₄ and N₂ or NH₃ may be used as thesource gases.

The flexibility of CVD systems allows for contamination-free processingand a modification of plasma shape through tuning of the cavity, allowssynthesis of a wide variety of carbon allotropes.

The CVD method is apparently useful for nanotube electronic devicesynthesis and integration into more conventional electronicarchitecture, the supported catalyst imposes severe limitations on thescale and CNTs growth rate.

4. Thermal Chemical Vapor Deposition (CVD)

CVD is another popular method for producing CNTs in which a hydrocarbonvapor is thermally decomposed in the presence of a metal catalyst. Theprocess involves passing a hydrocarbon vapor (typically for 15-60 min)through a tube furnace in which a catalyst material is present atsufficiently high temperature (600-1200° C.) to decompose thehydrocarbon. CNTs grow over the catalyst and are collected upon coolingthe system to room temperature. The catalyst materials may be solid,liquid or gas and can be placed inside the furnace or fed in fromoutside.

High quality individual single-walled carbon nanotubes (SWNTS) have beenproduced via the thermal chemical vapor deposition (CVD) approach, usingFe/Mo or Fe nanoparticles as a catalyst.

The CVD process has allowed selective growth of individual SWNTs, andsimplified the process for making SWNT-based devices. CVD growth ofSWNTs at temperatures of 900° C. and above was described using Fe or anFe/Mo bi-layer thin film supported with a thin aluminium under layer.However, the required high growth temperature prevents integration ofCNTs growth with other device fabrication processes.

Related technology is described in U.S. Pat. No. 5,877,110 wherebycarbon fibrils are prepared by contacting a metal catalyst with acarbon-containing gas. The fibrils can be prepared continuously bybringing the reactor to reaction temperature, adding metal catalystparticles, then continuously contacting the catalyst with acarbon-containing gas. Various complexities relating to feed rates,competing side reactions and product purity, among others, tend todetract from the wide-spread applicability and acceptance of thisapproach.

5. Flame Chemical Vapor Deposition (CVD)

Flames offer potential for synthesis of carbon nanotubes in largequantities at significantly lower cost than that of other methodscurrently available. By this technique, it has been shown in the artthat a premixed flame configuration operated at low pressure (20-97Torr), and burner gas velocity between 25 and 50 cm/s can be used. Avariety of fuels and fuel/oxygen compositions (C/O ratios) have beenexplored, including acetylene, benzene (C/O 0.86-1.00) and ethylene (C/O1.07) and diluent concentrations between 0% and 44 mol. These flames areall considered ‘sooting’ flames as they spontaneously generate condensedcarbon in the form of soot agglomerates suspended in the flame gases.Similarly, it has been reported that nanotubes may be produced in flamesunder sooting conditions. Samples of condensed material can be obtaineddirectly from the flame using a water-cooled gas extraction probe andalso from the water-cooled surfaces of the burner chamber.Nanostructures have also been extracted from the collected soot materialby sonication of soot material dispersed in toluene.

In 2000, the synthesis of single-walled carbon nanotubes in sootingflames at subambient pressures was reported. A partially-mixed flameconfiguration was used with fuel gases (acetylene, ethylene or benzene)issued through numerous small diameter tubes distributed through asintered-metal plate through which oxygen flows, drafting past the fueltubes. Iron and nickel compounds were vaporized and included in theflame feed as a metal catalyst precursor. Single-walled nanotubes wereobserved in acetylene and ethylene flames while multi-walled nanotubeswere observed in benzene flames.

It is widely agreed among those in the field that the more pressingissues for CNT technology relate to the availability, cost, and purityof CNTs. Currently, laser, arc, and chemical vapor depositionpreparation techniques have the crucial role of supplying researcherswith the material necessary for characterization of CNTs' properties andpredicting CNTs' applications. However, for industrial applications (inenergy storage or material reinforcement, for example) to become apractical and commercially-viable reality, a process which can producevery large quantities of quality CNTs will be required.

Those of ordinary skill in the art will be aware of certain flameprocesses that are frequently used in commercial manufacture due totheir many desirable features, including continuous processing (i.e.,volume production and scalability), energy efficiency, and capability ofsynthesizing and processing heterogeneous materials. The presentinvention seeks to apply and further develop prior art techniques incommercial flame technologies (e.g. the carbon black industry) into aunique process for the manufacture of nanoscale materials. (See, e.g.,U.S. Pat. No. 4,988,493 to Norman et al, and assigned to the assignee ofthe present invention.)

By using well defined, well-controlled multiple zone flames, the presentinvention in one aspect achieves a breakthrough in the ability tomanufacture commercial volumes of uniform high quality carbon nanotubesand other nanomaterials. This is believed to be a significantimprovement over early research using a commercial carbon black furnaceto produce carbon nanomaterials. (See, e.g., J. B Donnet et. al, “CarbonBlack and Fullerenes Part II: Precursor and Structure Identification” inKautschuk Gummi Kunststoffe, 1999, 340-343; M Pontier Johnson, et. al.“A Dynamic Continuum of Nanostructured Carbons in the CombustionFurnace” Carbon, 2002, 189-194.

SUMMARY OF THE INVENTION

In view of the foregoing and other considerations which will be readilyappreciated by those of ordinary skill in the art, the present inventionis directed in one aspect to an apparatus and associated methods forsynthesizing nanoscale materials, including carbon nanotubes.

In one embodiment, the invention involves propulsion of a combustible(e.g., hydrocarbon) gas through a torch nozzle to produce a flame. Thenozzle is positioned a selectable distance above a cooled substrate,upon which nanoscale materials, such as single-wall nanotubes,multi-wall nanotubes, “nano onions” (concentric spheres), andnano-diamonds are deposited.

In one embodiment, the flame is quenched and formation reactionsterminated by introducing a coolant in to the flame at a predeterminedreaction time, with the product collected by filtration from theresulting gaseous stream.

Notably, and in accordance with one embodiment of the invention, theflame may comprise multiple concentric or layered zones controlledindependently by differing mixtures of gases, each tailored to aspecific contribution to the process.

In one embodiment, the combustible gas is a mixture of oxygen (O₂) andacetylene (C₂H₂) in a predetermined and selectable ratio.

In another embodiment, a colloidal carbon material in the form ofspheres and of their fused aggregates, with sizes below 1000 nm, amaterial more commonly referred to as carbon black, is introduced intothe flame. An advantage of this embodiment is that the final productsare free of non-carbon catalyst residues, thus eliminating the need forcomplex purification steps. Further, the carbon black provides feedstockfor formation of the carbon nanostructures, functions as a solid state‘catalyst’ prior to being consumed by the nanotube formation, and can beused as a “template” for nanotubes of specific dimensions.

In another embodiment, other solid state catalysts can be used tosynthesize novel types of nanotubes and nanoscale materials, as will behereinafter described in further detail.

In accordance with one aspect of the invention, the synthesis processmay or may not involve introduction of a catalyst into an oxyacetyleneflame. One preferred catalyst is ferrocene (Fe(C₅H₅)₂), although it iscontemplated that many other catalyst materials may be employed. In apresently preferred embodiment, the catalyst is introduced into theflame by a carrier gas, such as argon.

In accordance with still another aspect of the invention, the synthesisprocess is highly tunable. Advantageously, numerous process parameterscan be controlled, such that various distinct species of end product canbe produced from a single reactor. Such process parameters include,without limitation: the catalyst (if any) used; the grade of carbonblack (if any) used; the mixture ratio of hydrocarbon gas used to feedthe flame; the flow rate of gases through the torch nozzle; the distancefrom the flame tip to the substrate; the composition of the substrate;the controlled temperature of the substrate; the deposition time; andothers.

As a consequence of the many controllable process parameters, the samereactor can be used to produce numerous different types of nanoscalematerials with differing properties including single-wall nanotubes,multi-wall nanotubes, nano-onions, and nano-diamonds. Empirical datashows that through careful control of process parameters, exceptionallyhigh consistency and purity in the final products can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features and aspects of the invention will be best appreciatedby reference to a detailed description of preferred embodiments thereof,when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a reactor system for synthesis ofnanoscale materials in accordance with one embodiment of the invention;

FIG. 2 is a side view of a torch nozzle used in the reactor system ofFIG. 1;

FIG. 3 is a side and end cross-sectional view of the torch nozzle fromFIG. 2;

FIG. 4 is a side cross-sectional view of the torch nozzle from FIGS. 2and 3 while operating to synthesize nanoscale materials;

FIG. 5 is a schematic representation of a vessel for containing catalystmaterial and for introducing catalyst material into a carrier stream;

FIGS. 6 a and 6 b are scanning electron microscope (SEM) and tunnelingelectron microscope images, respectively, of single wall carbonnanotubes produced in accordance with one embodiment of the presentinvention; FIG. 6 c is a plot of the Raman spectrum of the materialsdepicted in FIGS. 6 a and 6 b;

FIG. 7 a is a TEM image of SWNTs and MWNTs with carbon onions producedin accordance with one embodiment of the invention; FIG. 7 b is a plotof the Raman spectrum of the material depicted in FIG. 7 a;

FIG. 8 a is a TEM image of SWNTs produced in accordance with oneembodiment of the present invention; FIG. 8 b is a plot of the Ramanspectrum of the material depicted in FIG. 8 a;

FIGS. 9 a and 9 b are SEM and TEM images of SWNTs produced in accordancewith one embodiment of the present invention; FIG. 9 c is a plot of theRaman spectrum of the material depicted in FIGS. 9 a and 9 b;

FIG. 10 is an SEM image, and FIGS. 11 a and 11 b are TEM images ofmulti-wall and single-wall nanotubes produced in accordance with oneembodiment of the invention; FIG. 10 d is a plot of the Raman spectrumof the material depicted in FIGS. 10 a through 10 c;

FIGS. 11 a and 11 b are SEM and TEM images, respectively, of multiwallnanotubes produced in accordance with one embodiment of the invention;FIG. 11 c is a plot of the Raman spectrum of the material depicted inFIGS. 11 a and 11 b;

FIG. 12 a is an SEM image of MWNTs produced in accordance with oneembodiment of the invention; FIG. 12 b is a plot of the Raman spectrumof the material depicted in FIG. 12 a;

FIG. 13 is a TEM image of SWNTs produced in accordance with oneembodiment of the invention;

FIG. 14 is an SEM image of MWNTs produced in accordance with oneembodiment of the invention;

FIGS. 15 a and 15 b are SEM images of nano and micro diamonds producedin accordance with one embodiment of the invention; FIG. 15 c is a plotof the x-ray diffraction analysis of the material depicted in FIGS. 15 aand 15 b; and

FIGS. 16 a and 16 b are SEM images of nano and micro diamonds producedin accordance with one embodiment of the invention; FIG. 16 c is a plotof the Raman spectrum of the material depicted in FIGS. 16 a and 16 b.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the disclosure that follows, in the interest of clarity, not allfeatures of actual implementations are described. It will of course beappreciated that in the development of any such actual implementation,as in any such project, numerous engineering and technical decisionsmust be made to achieve the developers' specific goals and subgoals(e.g., compliance with system and technical constraints), which willvary from one implementation to another. Moreover, attention willnecessarily be paid to proper engineering practices for the environmentin question. It will be appreciated that such a development effort mightbe complex and time-consuming, but would, nevertheless, be a routineundertaking for those of ordinary skill in the relevant fields.

FIG. 1 is a schematic diagram of an apparatus for synthesizing nanoscalematerials in accordance with one embodiment of the invention. Theapparatus of FIG. 1 includes a torch nozzle 1, a substrate 3, awater-cooled holder 4, a mass flow meter 6, a water valve 7, a catalyst8, and a pyrometer 2. Various components of the system are controlled bymeans of a computer 5.

A premixed acetylene/oxygen flame burner in ambient atmosphere forms thebasis of the invention. All gas flow rates are regulated by mass flowcontrollers. In accordance with one aspect of the invention, the hightemperature of oxyacetylene flames, about 3000° C., ionizes thehydrocarbon gas by thermal plasma, thus generating the chemical vaporspecies. A multiple concentric or layered flame with each zonecontrolled separately by varying gas mixtures results in the synthesisof specific nanotubes and other nanoscale materials.

The ratio of acetylene, or other hydrocarbon, to oxygen is believed tobe important for optimizing conditions for synthesis and deposition ofcarbon nanotubes, diamonds or other nanoscale materials, and ispreferably maintained hydrocarbon rich. Other hydrocarbons have beensuccessfully utilized as feedstocks, with the advantage of improvedproduction economics.

Nanotube formation in a flame is promoted by injection of solidparticles or metallic ions. Ferrocene or nickelocene may be used as thesource of metal necessary for nanotube synthesis with the vapor suppliedto the premixed feed gases via a temperature controller. In accordancewith one aspect of the invention, carbon black particles have also beenused successfully to promote nanotube formation, either as ball-milledpellets or as particles formed in situ in a separate zone of the flame.

In one embodiment, argon may be used as carrier gas for the solidcatalyst, and to control the quantity of catalyst entering the flame.The deposition temperature is preferably measured and controlled usingan infrared pyrometer under control of the computer 5.

The distance between the torch nozzle and the substrate, which alongwith flow rates control reaction time prior to deposition, is carefullycontrolled. The deposition times are also carefully controlled.

FIGS. 2 and 3 show a torch nozzle 1 in accordance with one embodiment ofthe invention. In an exemplary embodiment, which is by no means limitingwith respect to the overall scope of the invention, the torch nozzle 1consists of a 10 mm diameter copper tube with six uniformly spaced, 0.3mm diameter holes at the tip surrounding one central orifice of 2 mmdiameter. The torch is preferably attached to an x-y-z translationsystem for positioning the torch nozzle 1 relative to the substrate.

EXAMPLES Example 1

The torch is moved vertically by the manipulator and the substrate ismoved horizontally by the substrate holder. Acetylene was supplied at asupply rate of 1 l/min and oxygen gas was supplied at a supply rate of1.2 l/min. The substrate surface was maintained at a temperature of 500°C. This condition was continued for one minute to thus produce a carbonnanotubes on the substrate.

The product formed on the substrate was examined by Raman spectroscopy,Scanning Electron Microscopy (SEM) and by Transmission ElectronMicroscopy (TEM). Those of ordinary skill in the art will appreciatethat the Raman spectra of carbon nanotubes have several distinctivepeaks located between 0 and 3000 cm⁻¹. The first major peak occurs atabout 1353 cm⁻¹ and the second occurs at 1583 cm⁻¹, and they arereferred to as the D peak and the G peak, respectively. The G peak isthe only first-order Raman peak observed in the spectrum of highlyordered pyrolytic graphite (HOPG). However, a modest amount of latticedisorder and clustering of carbon particles within the carbon structuregives rise to the D peak or the disorder-induced peak. The intensity ofthe D peak (I_(D)) and the G peak (I_(G)) are defined as the height ofthe peaks, and they can be measured in the Raman spectra. The Ramanpeaks located between 0 and 3000 cm⁻¹ are referred to as the first-orderRaman spectrum of carbon nanotubes. Beside the D and G peaks, there areseveral smaller peaks occurring at 218 and 398 cm⁻¹. These Raman peaksare characteristic features arising from the A_(1g) breathing mode ofsingle-wall carbon nanotubes with diameter range 0.7-1.5 nm. Thisobservation suggests that a quantity of single-wall nanotubes may havebeen deposited by this technique.

Examples

Extensive laboratory experimentation, refinement, and validation of theefficacy and utility of the present invention have been conducted. Thefollowing summarizes exemplary results of such experimental activity.

In particular, FIGS. 6 a and 6 b are scanning electron microscope (SEM)and tunneling electron microscope images, respectively, of single wallcarbon nanotubes produced in accordance with one embodiment of thepresent invention; FIG. 6 c is a plot of the Raman spectrum of thematerials depicted in FIGS. 6 a and 6 b. In this example, the SWNTs wereproduced with a diameter of 1.8 nM, as can be observed in FIG. 6 b,using aerosolized ferrocene as a catalyst in a multi-zone, single flame.The peak observable in FIG. 6 c evidences a high degree of purity ofSWNTs in the material produced in accordance with the invention underthe specified conditions.

FIG. 7 a is a TEM image of SWNTs and MWNTs with carbon onions producedin accordance with one embodiment of the invention; FIG. 7 b is a plotof the Raman spectrum of the material depicted in FIG. 7 a. In thisexample, the SWNTs and MWNTs have an average diameter of 2-5 nM, andwere produced using aerosolized ferrocene as a catalyst in a multizonesingle flame. The peaks observable in FIG. 7 c evidence the consistentpresence of SWNTs, MWNTs, and carbon onions in the material produced inaccordance with the invention under the specified conditions.

FIG. 8 a is a TEM image of SWNTs produced in accordance with oneembodiment of the present invention; FIG. 8 b is a plot of the Ramanspectrum of the material depicted in FIG. 8 a. In this example, theresultant SWNTs have an average diameter of 1.0 nM and were producedusing aerosolized ferrocene as a catalyst in a multizone single flame.The peaks observable in FIG. 8 b evidence a high degree of purity ofSWNTs in the material produced in accordance with the invention underthe specified conditions.

FIGS. 9 a and 9 b are SEM and TEM images of SWNTs produced in accordancewith one embodiment of the present invention; FIG. 9 c is a plot of theRaman spectrum of the material depicted in FIGS. 9 a and 9 b. In thisexample, the resultant SWNTs have an average diameter of 25-45 nM andwre produced using reclaimed carbon black as a catalyst in a multizonesingle flame.

FIG. 10 is an SEM image, and FIGS. 11 a and 11 b are TEM images ofmulti-wall and single-wall nanotubes produced in accordance with oneembodiment of the invention; FIG. 10 d is a plot of the Raman spectrumof the material depicted in FIGS. 10 a through 10 c. In this example,MWNTs and SWNTs with an average diameter of 5 to 35 nM were producedusing aerosolized carbon black as a catalyst in a multizone, singleflame.

FIGS. 11 a and 11 b are SEM and TEM images, respectively, of multiwallnanotubes produced in accordance with one embodiment of the invention;FIG. 11 c is a plot of the Raman spectrum of the material depicted inFIGS. 11 a and 11 b. In this example, the MWNTs have an average diameterof 5 to 85 nM and were produced using aerosolized carbon black as acatalyst in a multizone single flame.

FIG. 12 a is an SEM image of MWNTs produced in accordance with oneembodiment of the invention; FIG. 12 b is a plot of the Raman spectrumof the material depicted in FIG. 12 a. In this example, the MWNTs havean average diameter of 5 to 85 nM and were produced without the additionof a catalyst in a multizone single flame.

FIG. 13 is a TEM image of SWNTs produced in accordance with oneembodiment of the invention. In this example, the SWNTs were producedusing a methane-based catalyst in a multizone single flame. Ramanspectroscopic analysis shows peaks at 1600, 1319, 278, and 226 cm⁻¹,evidencing the purity of the material produced.

FIG. 14 is an SEM image of MWNTs produced in accordance with oneembodiment of the invention; In this example, the MWNTs were producedusing a methane-based catalyst in a multizone single flame. Ramanspectroscopic analysis shows peaks at 1584, 1335, 288, 239, and 225cm⁻¹, evidencing the purity of the material produced.

FIGS. 15 a and 15 b are SEM images of nano and micro diamonds producedin accordance with one embodiment of the invention; FIG. 15 c is a plotof the x-ray diffraction analysis of the material depicted in FIGS. 15 aand 15 b. In this example, the nano and microdiamonds are of the [100]orientation and have an average diameter of 10 to 100 μm, and wereproduced without the addition of a catalyst in a multizone single flame.The peak observable in FIG. 15 c evidences the purity of the materialproduced.

FIGS. 16 a and 16 b are SEM images of nano and micro diamonds producedin accordance with one embodiment of the invention; FIG. 16 c is a plotof the Raman spectrum of the material depicted in FIGS. 16 a and 16 b.In this example, the nano and microdiamonds are of the [111] orientationand have an average diameter of 10 to 100 100 μm, produce without theaddition of catalyst in a multizone single flame. The peak observable inthe Raman spectrum of FIG. 16 c evidences the purity of the materialdepicted in FIGS. 16 a and 16 b.

From the foregoing description of specific embodiments of the invention,it should be apparent that a method and apparatus for production ofnanoscale materials has been disclosed which shows great potential interms of scalability, reliability, purity, and economy, among otheradvantageous features. Although specific embodiment of the inventionhave been described herein in some detail, this has been done solely forthe purposes of illustrating various features and aspects of theinvention and is in no means intended to be limiting with respect to thescope of the invention as defined in the claims which follow. It iscontemplated that various substitutions, alternations, modifications,and process variations made be made relative to the embodimentsspecifically discussed herein without departing from the spirit andscope of the claims.

1. A method for synthesizing a carbon nanoscale material, said methodcomprising: propelling at least one stream of at least one combustiblegas through a nozzle; wherein the nozzle has at least one outlet; andwherein the at least one combustible gas is discharged from the at leastone outlet; igniting the at least one combustible gas to produce a flameat the at least one outlet; wherein igniting comprises burning the atleast one combustible gas to produce a chemical vapor species;introducing an aerosolized solid material comprising a colloidal carbonmaterial into the flame; and forming the carbon nanoscale material fromthe chemical vapor species in the absence of a metal catalyst.
 2. Themethod of claim 1, wherein the colloidal carbon material comprisescarbon black.
 3. The method of claim 1, further comprising: introducinga coolant into the flame at a predetermined reaction time.